Bread and cereal products are the predominate source of nutrition worldwide, supplying important nutrients such as protein, fiber, fats, carbohydrates, and vitamins. In addition to the nutritional advantages of grain based products, it is believed that diets high in grain products may reduce the risk of diseases such as heart disease, stroke, and certain cancers. Despite the dietary advantages of breads and cereals, it has been estimated that only one in ten U.S. consumers eat the USDA's recommended 6 to 11 daily servings of grain-based foods.
Further contributing to the deficiency of grain nutrition in the U.S. is the consumers' preference for certain grain products which have only low to moderate levels of protein and fiber. For example, white breads, which are made from flour having up to 30% of the whole grain removed, constitute the majority of all bread consumed in the U.S. Similarly, consumers in the U.S. and elsewhere are increasingly receiving daily grain intake from snack foods which are high in sugars and starch with only minimal protein and fiber content.
Therefore, it has long been considered desirable to supplement bread products with additional quantities of protein and/or fiber to increase the intake of these nutrients per serving. Traditionally, the amount of additional protein and fiber that may be added to bread dough has been limited. It is widely recognized in the art that bread dough becomes unworkably tough and rubbery or does not properly rise when even small amounts of additional protein and/or fiber are added. The resulting bread products have been described as unacceptably rubbery, chewy, dense or low in volume.
Most bread products are made from wheat flour that has a protein content between 7% and 13%, primarily in the form of vital gluten. After the addition of all other bread ingredients, a typical bread product made from wheat flour has a total gluten content of only about 3-4% by weight. It is well known in the art to add vital gluten to bread flour or dough in order to supplement the protein content of the resulting bread product. However, only relatively small amounts of vital gluten can be added before the dough becomes unworkable.
The rubbery and tough dough characteristic of added vital gluten result from the “knitting” or “development” of the vital gluten upon hydration as it is mixed with water to form dough. Vital gluten knitting has traditionally been considered to arise from disulfide cross-linking between gluten proteins. More recently, it has been discovered that cross-linking of tyrosine residues in wheat gluten proteins may also contribute to gluten development. See Tilley et al, J. Agric. Food Chem. 2001, 49, 2627-2632. The knitting of vital gluten produces the visco-elastic properties characteristic of most bread dough. The elasticity of the dough allows gas bubbles formed by yeast in leavened bread to be retained in the dough. In this manner, vital gluten permits the dough to rise. When additional amounts of vital gluten are added to flour or dough to supplement the protein content, excessive knitting of the protein molecules reduces the elasticity of the dough, resulting in the deleterious effects on the dough and bread properties described above. Due to these limitations, it was heretofore possible to add only about 3-5% by flour weight of additional vital gluten to a leavened bread product. The resulting gluten supplemented bread products contain a total protein content of only about 8% by weight per loaf.
Prior approaches to increasing the protein content of bread products include adding non-fat dry milk (NFDM) to the dough as a source of additional whey protein. See e.g. U.S. Pat. No. 5,458,902 (“Rudel”). The whey proteins in NFDM do not “knit” to the high degree associated with vital gluten allowing for somewhat more workable dough. Breads supplemented with NFDM are reported achieve total protein contents of 20-24% by weight. However, the use of NFDM suffers the disadvantage of introducing dairy ingredients not typically associated with bread products. Such bread products are not acceptable to consumers that have difficulty digesting lactose, are allergic to milk products, or otherwise do not desire breads made with milk products.
Other approaches to increasing protein content in bread have involved denaturing proteins to reduce knitting, diluting flour with large quantities of fiber to offset the added protein, or adding reducing agents to disrupt disulfide bond formation. Typically, vegetable gums must be added in these processes to mimic the moisture and volume of a normal bread product. These approaches have had only limited success in increasing the protein content of bread products and produce breads with commercially unacceptable taste and texture.
Similar limitations on the amount of fiber that can be added to a bread product are well known in the art. Bread products have been supplemented with a variety of dietary fibers such as alpha cellulose, in order to increase the total fiber content. However, the quantity of additional fiber that may be added has heretofore been limited by the unworkable dough and the unacceptable texture and volume of the resulting breads.
Accordingly, there is a continuing need in the art for grain products having high total protein and/or fiber content.